1. Field of the Invention
This invention pertains to automatic high-speed labeling machines. More particularly, the present invention relates to automatic high-speed labeling machines for labeling cylindrical containers which are linerally fed through the machine in a straight line, but are caused to rotate about their vertical axes through a point of contact with a rotating cylindrical label transporting drum which results in the transfer of a label to a container and thereby causing the container to wrap said label around itself.
2. Description of the Prior Art
The prior art is replete with descriptions of labeling machines for cylindrical containers which all accomplish the same purpose but by different means.
For example, in U.S. Pat. No. 4,108,710 (1978), Hoffman describes a high-speed labeling apparatus for cans which are fed into and clamped onto the periphery of a rotating drum which moves individual cans past a first adhesive station where an adhesive is applied to each can at a predetermined location thereon and the cans are then moved on to a labeling station. Labels, previously cut from a continuous strip, are held by a pourous rotating vacuum disc or drum whereon the trailing edge of said label receives adhesive and then it is moved into position where the leading edge of said label engages a can at the location of adhesive on the can. As both can and label are moving in the same direction and at the same speed, the vacuum hold on the label is released thereby allowing the label to move away with the can to a wrapping station where the can is released and rolled along a track by a gripping conveyor belt thereby wrapping the label and its trailing edge around the can. This so-called "flagging" method of labeling was the state of the art for many years and was commonly used in the labeling of soup cans, however the flagging method, as described, is essentially limited to containers which can be gripped by the rotating drum in a manner that adhesive may be applied to the container while it travels through the machine for wrapping by a sturdy label such as paper.
In U.S. Pat. No. 4,500,386 (1985), Hoffman discloses a "roll-on" pad opposite and concentric to a rotating vacuum drum between which cylindrical containers are fed by a rotating star wheel. As the container comes into tangential contact with the rotating vacuum drum, a glue-containing label held on the drum is transferred to the container and the container is rotated about its vertical axis by the drum causing the label to be pressed onto said container by the roll-on pad. However, the path of the containers while under control of the star wheel is an S-shaped path which requires change of direction including an inflection at the point of transfer at the point of transfer from the star wheel to the vacuum drum and roll-on pad, and these changes of direction impose acceleration and loads which limit the speed of labeling.
In U.S. Pat. No. 4,714,515 (1987), Hoffman describes a "straight line" container labeling apparatus including oppositely moving main drive and porous labeling belts, and a timing star and second star wheel having rollers on the ends of its arms for engaging and aligning each container while allowing it to rotate freely between the belts. In this apparatus, the leading edge of a continuous strip of label stock is gripped by a radially retracted vacuum pad located on the periphery of a rotating vacuum drum and pulled until a cutting knife carried directly on the drum severs the trailing edge of each label. The retracted vacuum pads are selectively extendable for application of adhesive and then may be retracted to allow fingers to strip each gummed label from the drum and transfer it to a vacuum wheel over which is entrained a porous labeling belt that carries each label to a container driven by the drive belt and aligned by the second star. Although workable in theory, this fairly complex labeling apparatus obviously required critical synchronization of its interrelated elements to function properly. During high speed labeling operations (more than 125 containers per minute) several problems arose. For example, containers would often jam as they left the timing star and became wedged by an arm of the aligning star. Additionally, the reciprocating vacuum pads on the vacuum drum did not provide a uniform glue pattern on the labels which often caused glue to be deposited on the porous labeling belt resulting in labels stuck thereon. Moreover, part of the cutting means was located on the periphery of the vacuum drum which, of course, increased in rotational speed with the speed of the labeling operation, and often resulted in improperly cut labels. Thus, the labeling apparatus as above described was short lived in actual high speed production and is not known to be in use today.
In U.S. Pat. No. 4,931,122 (1990), Mitchell discloses another straight through labeling machine with a "feed-screw" for moving cylindrical containers past, but in tangent to, a vacuum drum containing precut gummed labels. The containers travel along a guide-way to the feed screw where they also contact an endless belt causing the containers to spin counter-clockwise around their vertical axes. As the feed screw advances the containers linearly past, but in tangent to, the vacuum drum, a label is transferred to a container and is preferrably wrapped around it before said container exits the feed screw. Although this labeling machine appears to be an improvement over the cited prior art, the counter-clockwise rotation of the containers while being linearly advanced within the feed screw causes vertical drag or a retarding force acting on the containers due to friction which is undesirable in high speed labeling operations.